The present invention relates to a cement for the fixation of osseous prostheses.
It is known that the problems raised by the treatment of diseases such as arthrosis or degenerative joint disease of the hip have in recent years been able to be solved by surgical operations which consist in removing the affected parts of the joint and in replacing them by metal, ceramic or plastic prostheses in order to provide the coefficients of friction compatible with correct functioning of the joint. In the case of the hip, the prostheses are fixed, on the one hand, in the medullary cavity of the femur and, on the other hand, in the acetabulum of the pelvis.
Up to the present time, this fixation has been effected by means of polymer cements, obtained by mixing a methyl polymethacrylate powder with monomer methyl methacrylate, a catalyst and possibly barium sulfate as opaquing agent.
However, such cements are not completely satisfactory from the medical point of view; in fact, methyl methacrylate has a certain toxicity; furthermore, too much heat is emitted when these cements harden, this leading to relatively high temperatures of the order of 80.degree. to 90.degree. C. and, in addition, there is a phenomenon of shrinkage during polymerization.
On this subject, it should be noted that the use of cements based on synthetic resins raises certain problems due to the exothermicity of the hardening reactions and the phenomena of shrinkage of the resin during hardening. Thus, although cements based on synthetic resins have already been used in other fields, particularly in the dental field, said cements are generally not suitable for the fixation of osseous prostheses, as the characteristics required for these two uses are different. In fact, for the fixation of osseous prostheses, shrinkage of the resin must be reduced as far as possible and it is necessary to use cements of which the hardening does not lead to a reaction which is too exothermic in order to limit the heating all the more so as, in this case, larger quantities of cement are used than in the dental domain. Furthermore, for the fixation of osseous prostheses, it is necessary to use cements capable of hardening in a moist medium whilst in the dental art the problem is not the same, since it is possible to use local drainage techniques.
Finally, for the fixation of osseous prostheses, the consistency of the cement is of great importance to obtain a rapid and sure positioning of the cement between the elements to be fixed. Moreover, it is advantageous to obtain the hardening of the cement relatively rapidly once it is placed in position.